Field of the Invention
The present disclosure relates to a local dimming method and a liquid crystal display using the same.
Discussion of the Related Art
The application of a liquid crystal display has increased due to its characteristics of light weight, compact size, low power consumption operation, etc. A backlit liquid crystal display displays images by controlling an electric field applied to a liquid crystal layer to modulate light received from a backlight unit.
The picture quality of a liquid crystal display depends on contrast. There are limitations in improving the contrast only by modulating transmittance of a liquid crystal layer of the liquid crystal display. To solve this problem, a backlight dimming method for adjusting the brightness of a backlight depending on image has been developed so as to remarkably improve the contrast of the liquid crystal display. The backlight dimming method can reduce power consumption by adaptively adjusting the brightness of the backlight depending on input image. The backlight dimming method includes a global dimming method that adjusts the brightness of the overall display screen and a local dimming method that divides the display screen into a plurality of blocks and independently adjusts the brightness of the blocks.
The global dimming method can improve a dynamic contrast measured between a previous frame and the next frame. The local dimming method can locally adjust the brightness of the display screen within one frame period so as to improve a static contrast that is difficult to enhance by the global dimming method.
The local dimming method segments a light-emitting face of a backlight into a plurality of blocks, and increases a backlight luminance of a block corresponding to a bright image while decreasing a backlight luminance of a block corresponding to a relatively dark image. As shown in FIGS. 1A, 1B and 1C, the local dimming method can control the backlight luminance more accurately when the number of segmented blocks of the light-emitting surface of the backlight increases. On the other hand, a luminance contribution degree of one block decreases when the number of segmented blocks increases, as shown in FIGS. 1A, 1B and 1C.
A dimming value for each block in local dimming may be determined by a spatial filter. The spatial filter can improve undesired halo effect and luminance non-uniformity by diffusing a peak luminance of a backlight to surrounding blocks to reduce the spatial frequency of the backlight luminance. A conventional spatial filter has a fixed mask size and a fixed mask coefficient. Accordingly, a local dimming method using the conventional spatial filter decreases the backlight luminance when the number of segmented blocks of the light-emitting surface of the backlight increases. This darkens displayed images.